How can I reuse a class between a few addons
Inside your scripts folder you have addons and maybe addons_contrib and a modules folder. 



The modules folder can added if it's not there and used to store files that you want to access from various add-ons. In this case I have a file which stores functions, but it could store classes (anything a .py file is used for).

Imagine the modules folder has a folder inside called 'some_name', 



and some_name contains a python file called functions, 



so the path is scripts/modules/some_name/functions.py . To import that module in an addon you write

from some_name import functions




Potentially this makes installing your add-on a little bit more involved for the average novice user, unless you write code that places the files in the modules folder automatically